It is located in the district of Siegen-Wittgenstein in the Arnsberg region. The university town (18.600 students in the 2013–2014 winter semester) is the district seat, and is ranked as a "higher centre" in the South Westphalian urban agglomeration.

In 1975, in the process of municipal reforms and amalgamations, Siegen's population exceeded the 100,000 mark.